1. Field of the Invention
This invention relates to the detection of carbonaceous materials or materials geologically associated therewith. More particularly, it relates to the location of subterranean geological deposits of carbonaceous materials or materials geologically associated therewith, such subsurface earth formations are often referred to as source formations or migration paths. By "carbonaceous materials" as used herein is meant petroleum, coal, natural bitumens, including tars and asphalts, partially carbonized animal and vegetable matter and carbonaceous geological deposits and formations including oil-bearing shales. Further, this invention relates to a method for distinguishing crude petroleum carbonaceous materials from coal or shale carbonaceous materials on subsurface earth formation materials.
2. Prior Art
Prior to this invention, there has been no practical way of directly detecting the presence of very small quantities of carbonaceous materials on samples of subsurface earth formation materials. Further, if small quantities of such materials were detected, there was no practical way of positively distinguishing within such detected carbonaceous materials those materials which are crude petroleum based materials.
Representative of the prior art in the field of prospecting for petroleum are U.S. Pat. No. 2,686,108, W. S. Hoffmeister, issued Aug. 10, 1954, for Microfossil Prospecting for Petroleum, where a process is disclosed for identifying sediments from bore hole samples; U.S. Pat. No. 3,305,317, J. E. Cooper et al, issued Feb. 21, 1967, for Method of Prospecting for Petroleum, where a process is disclosed for analyzing ground waters for certain carbon atoms and comparing the ratio of certain of those identified carbon atoms as a means for identifying a petroleum reservoir; U.S. Pat. No. 3,343,917, G. M. Friedman, issued Sept. 26, 1967, for Obtaining Paleoenvironmental Information, where a process is disclosed for prospecting for petroleum by collecting and analyzing sedimentary rock for carbonate minerals; and U.S. Pat. No. 4,093,420, J. F. Grayson et al, issued June 6, 1978, for Mineral Prospecting By Organic Diagenesis, where a method of prospecting is disclosed for collecting and analyzing geological samples to produce anomalies characteristic of subsurface formations.
Each of the foregoing prior art methods measures a characteristic or a constituent that is representative of the presence of crude oil or is typical of the formations containing crude oil. None measure signals directly from crude oil itself.
Various methods are known for detecting the presence of carbonaceous materials, including, in increasing order of sensitivity, stain chemistry (adding chemicals to a sample to detect a change in color when carbonaceous materials are present); distillation treatment (as in chromatography where the presence of distillation fractions are detected); fluorescence (the irradiation with selected wave length electromagnetic energy to cause certain constitutents to fluoresce); and nuclear or electron spin resonance (the identification of spinning atomic particles in the constituents of the carbonaceous materials). The most sensitive of the foregoing techniques is electron spin resonance (ESR) where the presence of unpaired electrons in atomic structures are identified by subjecting samples of the structures to controlled magnetic and electromagnetic fields.
With the use of ESR techniques, it is possible to detect the presence of very small traces of carbonaceous materials; however, it is not possible to distinguish the type of carbonaceous material, i.e., crude petroleum, coal, tar sand or shale, from which the ESR signals were derived. ESR signals from geological materials may be attributable to a number of carbonaceous materials, both natural and refined, thus further confusing the attempt to identify a carbonaceous material.
The present invention uses ESR plus techniques for distinguishing the ESR signal of crude petroleum based natural carbonaceous materials as a method for detecting the presence or past presence of such materials in an exploration method.